Changes in visual cortical function in moderately myopic patients: a functional near‐infrared spectroscopy study

Abstract

PurposeTo investigate haemoglobin oxygenation in the visual cortex of myopic patients using functional near‐infrared spectroscopy (fNIRS).MethodsThe experiment consisted of two parts. Part 1 examined functional changes in the visual cortex before and after refractive correction in myopic patients. Subjects were divided into normal controls, uncorrected and corrected myopes. Part 2 examined functional changes in the visual cortex caused by lens‐induced myopia in normal subjects, and whether this activity recovered after a period of rest. Here, subjects were divided into three groups: emmetropes, lens‐induced myopia and a rest group. The rest group completed a test with the uncorrected eye following lens removal and 5 min of rest. The visual stimulus was a black and white checkerboard. fNIRS was used to detect changes in oxyhaemoglobin content within the visual cortex. The original fNIRS data were analysed using MATLAB to obtain the β values (the visual cortical activity response caused by the task); these were used to calculate Δβ, which represents the degree of change in oxygenated haemoglobin caused by visual stimulation.ResultsThe Δβ value measured in each single channel or only in the region of interest (ROI) was significantly higher in the emmetropic control group than the uncorrected myopic group. After optical correction, the responses of myopic subjects approached those of the emmetropes and were not significantly different. If myopia was induced in emmetropic subjects by imposing defocus with positive lenses, a decline in functional activity was observed similar that observed in uncorrected myopes. Activity recovered after the lenses were removed.ConclusionsMyopic defocus reduced the level of haemoglobin oxygenation in the visual cortex, but activity could be restored by optical correction.

Functional Near-Infrared Spectrometry as a Useful Diagnostic Tool for Understanding the Visual System: A Review

“…However, visual cortical function can be restored with optical correction, as measured by fNIRS [20]. This literature illustrates the usefulness of fNIRS in establishing a further understanding of the eye generally.…”

“…A recent study compared the degree of change in oxygenated hemoglobin caused by visual stimulation in emmetropic and myopic participants [ 20 ]. When comparing emmetropic and uncorrected myopic participants, the degree of change was higher in emmetropic participants.…”

“…These results indicate that myopic defocus tends to reduce the level of oxygenated hemoglobin and functional activity in the visual cortex. However, visual cortical function can be restored with optical correction, as measured by fNIRS [ 20 ]. This literature illustrates the usefulness of fNIRS in establishing a further understanding of the eye generally.…”

The impact of visual environment on the evolution of myopia

“…[12]It is a major public and economic health burden worldwide. [20][21]According to several teams of researchers and Optometry professionals in Europe, the United States, and Asia, the parameters potentially involved in this Planetary epidemic concern [20][21] are genetics [3] and environmental factors such as generalization and lengthening of Schooling and sedentary lifestyle, which seem to be the root of the problem. Added to that is the correction of Ametropia by spherical concave glasses [12] which only corrects the central myopia Defocusing leaving behind the peripheral hyperopic defocusing.…”